Exemplary embodiments are directed to techniques used during the treatment of Atrial Fibrillation (AF). Atrial fibrillation is the most common sustained arrhythmia, which currently affects two million Americans. Atrial fibrillation is associated with increased mortality, morbidity and an impaired quality of life, and is an independent risk factor for stroke. The substantial lifetime risk of developing atrial fibrillation underscores the public health burden of the disease, which in the United States alone amounts to an annual treatment cost exceeding $7 billion.
Eighty-five percent of episodes in patients with atrial fibrillation are known to be triggered by focal electrical activity originating from within muscle sleeves that extend into the Pulmonary Veins (PV). Atrial fibrillation may also be triggered by focal activity within the superior vena cava or other atrial structures. These focal triggers can cause atrial tachycardia that is driven by reentrant electrical activity and rotors, which may then fragment into a multitude of electrical wavelets that are characteristic of atrial fibrillation. Prolonged atrial fibrillation can cause functional alterations in membrane ion channels as well as alterations in ion channel expression. These changes further perpetuate atrial fibrillation.
Radiofrequency (RF) ablation is an effective therapy for treating atrial and ventricular rhythm disturbances. Nearly 100,000 RF ablation procedures are performed annually in the United States to treat cardiac arrhythmias. RF ablation targets the key elements of reentrant pathways and/or abnormal ectopic loci without damaging significant amounts of adjacent healthy myocardium and coronary vessels. Ablations are also done with cryo-ablation and laser guided ablation systems.
To perform an RF ablation procedure, a catheter is threaded into the heart and the tip is guided into the atria. A transseptal puncture is made to allow cross-over from the right atrium into the left atrium where the crux of the ablation is performed. The catheter then emits a pulse of high-energy RF electricity that damages atrial tissues and forms scar tissue that blocks abnormal signals. The most common RF ablation treatment of atrial fibrillation consists of placing ablation lesions in a circular fashion around the ostium of each pulmonary vein. The lesions electrically isolate the pulmonary veins to block focal triggers from entering the left atrium. RF lesions can also be placed epicardially during minimally invasive or open heart surgery.
The extent of RF ablation lesions is not simply a function of delivered RF energy, but depends on many factors, including the contact between the catheter tip and the tissue, the thickness of the myocardium, the degree of blood flow, and the presence of fat. Currently we use surrogates to determine anatomy known as 3D mapping systems (CARTO and NAVEX), surrogates can be off by 1 or 2 cm. Current electro-anatomical mapping systems map mainly the physical location of the catheter tip but not the extent of cell injury caused by the ablations. Therefore, as of today, RF ablation lesions are created with no information regarding the physiological condition of the affected tissue. This is problematic considering that gaps of excitable tissue between ablation lesions are directly related to arrhythmia recurrences. Monitoring tissue injury produced by ablation in real time remains a major limitation of current ablation approaches.
To resolve the problem of incomplete lesions, two main strategies have been proposed. The first is to improve ablation devices, which includes the development of multi-polar and linear catheters, balloon-based technologies using lasers and high-intensity focused ultrasound, as well as pressure-sensor equipped RF catheters.
The second strategy is to visualize RF ablation lesions during the ablation procedure. Such visualization can be based upon acute changes in the chemical and/or physical properties of the damaged tissue. Specifically, the current visualization proposals require the use of a dye and include magnetic resonance imaging (MRI), coherence tomography (CT) and spectroscopy.
All these strategies use surrogates to predict the areas of the gaps and none has a real time direct visualization technique as we have designed. Despite all the current technology, pulmonary vein reconnections occur in 94% of patients after the first procedure. Atrial fibrillation recurrences after ablation procedures are 80-90% of the time due to pulmonary vein reconnection at the sites of gaps.